The present invention is directed to a fastener with a plastic head assembled therewith. More particularly, the present invention is directed to an improved plastic-headed fastener assembly capable of withstanding the high torques associated with self-drilling and self-tapping fasteners. The plastic head overlies and protects the metal head therebeneath from corrosion, usually has a color which is coordinated with the panel being attached, and is designed so that the rotational torque forces are transmitted by the plastic to metal surfaces as taught in commonly assigned U.S. Pat. No. 4,041,834. U.S. patented application Ser. No. 81,496 filed Oct. 12, 1979, which is also commonly assigned, is directed to an improved plastic-headed fastener assembly making it related to, although it is distinctly different from, the invention of the present application.
A problem has been encountered with the fastener assembly of the abovenoted patent when the assembly is used to drill and/or tap a first relatively thin panel followed by a second comparatively thick member. The tapping of the thin panel is sometimes completed before the completion of the tapping of thicker member. Consequently, the thin panel "climbs" the threads of the fastener coming into engagement with the plastic head. Contact between the plastic and metal for prolonged periods during high-speed rotation creates large amounts of heat due to friction. This heat is sometimes sufficient to cause damage to the plastic head due to melting. Consequently, the fastener assembly may not seat or seal properly and, sometimes, the plastic head may be severely damaged to the point where it will fall off, leaving the metal head unprotected.
The improved assembly overcomes these problems. The plastic head has a first outer sealing flange extending outwardly and downwardly from the metal head which underlies the plastic. A second inner sealing flange extends downwardly a distance exceeding the downward extension of the outer flange and at a position spaced outwardly from the threads by several times the thickness of the thin panel. As the thin panel climbs the threads of the fastener it will engage the second inner sealing flange and its upward motion will be stopped. The edge of the hole will continue to be drawn up inside the second flange causing the hole to be stripped out (i.e., enlarged to a point where thread-engagement is no longer possible). The thin panel is now free to fall back down into contact with the thick member. Even failing this, the thin panel is no longer being drawn into snug, high-friction contact with the pastic head. Therefore, the potential for damage (which by this design, is limited to the area of the second flange) is now dissipated.
These and other features, advantages and objects of the present invention will be more thoroughly understood following a reading of the attached specification when taken in conjunction with the accompanying drawings.